Chapter Nine
Vibration-based Anti-Biofouling of
Implants
Po Ying Jacob Yeh
,‡
, Jayachandran N. Kizhakkedathu
and Mu Chiao
Department of Mechanical Engineering, 2054-6250 Applied Science Lane,
University of British Columbia, Vancouver, B.C., Canada.
E-mails: ypy0816@interchange.ubc.ca,
§
muchiao@mech.ubc.ca
Centre for Blood Research and Department of Pathology and Laboratory Medicine,
4th Floor, Life Sciences Centre, 2350 Health Sciences Mall, University of British
Columbia, Vancouver, B.C., Canada.
E-mail: jay@pathology.ubc.ca
The interfacial behavior of proteins at surfaces has attracted much attention over the
years because of the problem of fouling, which is encountered in implants, microfiltar-
tion membrane, medical implantable devices, drug delivery system and biosensors.
A novel anti-biofouling mechanism based on the combined effects of electric field
and shear stress is reported. The mechanism was observed in mm scale piezoelectric
plates coated with different metal materials and MEMs (MicroElectroMechanical
system) fabricated membrane based device. Experimental observation of quantity
of proteins adsorption and theoretical calculations of protein-surface interactions
(van der Waals (VDW), electrostatic, and hydrophobic) and shear stress reveal the
mechanism for protein desorption from surface. This anti-fouling mechanism is also
able to implant to micromachined MEMs membrane. The dimension of membrane
(Si(2 μm)/SiO
2
(1 μm)) is 2000 μm × 500 μm × 3 μm. The membrane vibrates in a
flexural plate wave (FPW), which is further verified by finite element simulation. The
surface charges on the membrane and the fluid shear stress contribute in attenuating
the protein adsorption on the membrane surface. Potentially, a microelectromechani-
cal system (MEMS)-based vibrating membrane could be a tool to minimize biofouling
of in vivo implants.
9.1 INTRODUCTION
The success of implantable device technologies, such as artificial joint, vascu-
lar graft, cardiopacemaker, cardiovascular, drug delivery system, and biosensor,
Biomaterials for MEMS, Edited b y M. Chiao and J.-C. Chiao
Copyright © 2011 by Pan Stanford Publishing Pte. Ltd.
www.panstanford.com
978-981-4241-46-5
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204 P. Y. J. Yeh, J. N. Kizhakkedathu and M. Chiao
had improved the patients’ life quality. However, with the advances of these
technologies, the view of biocompatibility had extended from the “the host tol-
erates the device” to “the device tolerates the host and vice versa”.
1,2
For example,
a subcutaneous glucose sensor comprises of immobilized enzymes, electrodes and
a semi-permeable membrane. The semi-permeable membrane acts as a protecting
layer that keeps the enzyme and electrodes from the attack of the immune system
and it allows glucose from interstitial space to diffuse through. In order to be
successful, the semi-permeable membrane must not induce pathogenic reactions
to the host. On the other hand, the glucose permeability of the membrane must be
maintained at all times. Hence, the problem of biofouling needs to be reduced as
much as possible.
Biofouling is a process started immediately after a foreign object comes into
contact with biological fluids because of the immune response system. And it is
considered to be one of the greatest challenges of medical implantation.
25
The
immediate response is to flood the injured area with blood followed by adsorption
of blood proteins onto the implant surface and activation of the molecular and
cellular defense systems.
6,7
The coagulation, complement, immune and inflamma-
tory pathways can all be initiated by this process as can platelet and white cell
activation. The extent to which these responses occur depends on the nature of
the protein adsorption, specific binding or rejection reactions that occur at the
impalnt-blood interface. Usually an adsorbed protein layer of thickness from
0.5 to 9 μm accumulates over time. Approximately 21 days after implantation,
an avascular fibrous capsule of up to 100 μm will form around the implant and
may reduce its performance.
8
Prevention of protein adsorption unto implants
is critical for increasing their longevity. Some methods had been provided so
far, such as polymer-based coatings,
919
plasma surface functionalization,
20
sur-
face charges,
21
detergent coatings,
22
nano-structured surfaces,
8
surface roughness
and topography,
23,24
mechanical vibration,
8,2527
and flow flushing upon the
surface,
28,29
etc. Coatings, surface roughness, surface topography are catalogued
as passive methods, while physical means, such as mechanical vibration and flow
flushing are considered as active methods of anti-biofouling.
Numerous studies have indicated that the surface chemistry of and
microstructure on the implant surface can modulate protein adsorption.
3,4,8,30
And
among those passive methods, polymer coating is attractive for certain applica-
tions, such as long-circulating sterically protected liposome,
31
biosensor,
32
and
protein chip.
33
Those polymer candidates usually are composed by three parts,
anchor to surface, monomer repeated backbone, and end functional group.
The most popular polymer used is probably the hydrophilic poly(ethylene gly-
col) (PEG). When there is sufficient high PEG graft density, the coiled PEG with one
end anchored to the surface will form brushes by extending the coils away from
surface, and so that to create a steric barrier from protein adsorption.
34,35
However,
polymer coatings are successful for short term and often fail in the case of a
highly complex mixture of proteins, for example, blood plasma,
9,13
or under in vivo
conditions.
5
As an alternative to polymer coating, researchers have also fabricated
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